The Refutation of Bohmian Mechanics

Demystifier

As I said, any and each one which strongly interacts with the measured system.

If no macroscopic measurement device is close to the measured quantum system, then no macroscopic measurement device can measure this quantum system (because there is no strong interaction). So in this case none of them is "correct".

The one (or more) which interacts strongly with the measured system, is the correct one.

That's true.

Maybe to you, but to me other interpretations of QM are even more counterintuitive.

Not exactly. Other devices and objects in the universe are also ontological, both before and after the measurement. However, only this particular device is strongly correlated with the microscopic degrees of the quantum computer. That's because, as I said many times above, only this particular device strongly interacted with the microscopic quantum-computer degrees.

Demystifier

Thanks, camboy! I see that your understanding of deBB is also very good.

A. Neumaier

Of course they are different. But the thesis about BM+quantum computing was using the statistical mechanics analogy.
No. There is nothing surprising in that we don't have thermal equilibrium. In statistical mechanics, The proof that equilibrium must be obtained is restricted to the very stringent assumption of ergodicity. Very few real systems are ergodic. Equilibrium is reserved for special sytems that are more or less homogeneous.
No. There must also be proof that entropy always increases, and that it increases to its maximum.
This is highly nontrivial in statistical mechanics, and wrong for most complex systems. Nature is full of systems that never reach the maximum entropy state.

It would be very surprising if the situation were different for quantum equilibrium, and that it is achieved without such stringent conditions. Can you point to an online source for the proof?

A. Neumaier

If I see that I was wrong, I correct myself immediately. Thus any state of being wrong is very short-lived. If I repeat assertions that seem wrong to you then only because your arguments did not convince me.
You have not the slightest idea about how much literature I have read and how much I am reading
while preparing my contributions to this forum.
Scientific dispute takes the free offering of information as a given that doesn't need special thanks.
I also do not expect being thanked for the information I provide on this forum.
Please take this back. I never said such a thing.
You seem to say a lot without first checking the facts. I am not a professor of quantum physics.
I didn't say such a thing.

A. Neumaier

But the system still has a dynamics. Though apparently not one easily described by BM.

Demystifier

OK, now we are at the territory of statistical mechanics. In statistical mechanics there is a Boltzmann H-theorem that provides that entropy never decreases. Perhaps this theorem is not perfectly rigorous (it does not use ergodicity), but in Bohmian mechanics there is an analogous equally (non)rigorous theorem that entropy measuring closeness to the quantum equilibrium also never decreases. So what we have in BM are
1) A theorem, probably not perfectly rigorous, and
2) Many explicit numerical simulations which agree with the theorem
I can agree that more work is needed in order to establish a completely satisfying proof, but the above is certainly a strong evidence (if not the proof).

Demystifier

Of course.

Why do you think so?

A. Neumaier

When we hear something, it can count as an observation, though no position variable is observed.

When we see a star, which position variable do we observe?

A. Neumaier

Because, as you said, none of the pointer variables is ''correct''. How else would you then describe the dynamics of an unobserved system of spins?

Demystifier

Oh, yes it is. When your ear hears something, the nerves in your ear vibrate. And vibration is nothing but a change of a POSITIONS of parts of an elastic object.

The position of nerves in the eye.

Of course, it's not that you really "observe" these positions in the psychological sense, but the point is that colors and sounds are ENCODED in the positions of something.

A. Neumaier

It assumes instead the Stosszahlansatz, which is taken as an unproved assumption.
(For a gas of hard spheres, the Stosszahlansatz can be justified by an ergodic theorem).

Moreover, stating that entropy doesn't decrease is very far from stating that entropy reaches its global maximum (the equilibrium state). For example, one can deduce from the Boltzmann equations in some approximation the Euler equations - there the total entropy is constant, but the dynamics is still highly nontrivial - very far from the equilibrium state. Thus the H-theorem says nothing at all about approach to equilibrium. (In simple terms: if I am climbing a hill and never go downwards, I can still end up anywhere above my current position, no matter how long I wait. No guarantee to reach the hill top.)

Finally, Boltzmann's approach only works for the classical ideal gas.
It is as much evidence for reaching quantum equilibrium as Boltzmann's H-therorem is evidence for the universe being in global equilibrium - nil!

Demystifier

Bohmian mechanics describes the dynamics of wave functions and particle positions, period. It does that both for observed and unobserved systems. However, Bohmian mechanics, at the fundamental level, does not describe the dynamics of spins or any other "observables". It is only in the context of specific measurements that certain configurations of particles and wave functions can be INTERPRETED as spins or other "observables".

Just as classical optics is only about electromagnetic waves and not about colors, even though some wavelengths can be interpreted as colors in specific measurement configurations.

Demystifier

With that I agree ...

... but with that I don't. Anyway, I am glad that now you have a clearer picture what BM, in its current state of development, has achieved and what it has not. Just because some branch of science is not fully developed yet, it is not a reason to abandon it.

A. Neumaier

Ah. So the only pointer variables that count are those in the head of people. For if we observe the pointer of an instrument, all we really observe is also the position of nerves in the eye?

And I never before heard that the nerves in the eye move in response to light. What moves are the electrons inside the eye. But these are not a ''POSITION variable (at the macroscopic level)''.

A. Neumaier

My question was - how, for an unobserved spin system. Your dogmatic position is of no help in answering that.

A. Neumaier

If the Boltzmann's H-therorem were any evidence for the universe being in global equilibrium then
e would observe this global equilibrium - which means we wouldn't exist, contradiction.

Thus the Boltzmann's H-therorem is no evidence at all evidence for reaching global equilibrium, and because you agreed to the first part of my statement, you have also no evidence for that the state of the universe reached quantum equilibrium in BM.

Demystifier

Not only they, but if you want to understand how something is observed by a human, then you cannot avoid them. They are crucial.

Irrespective of one's favored interpretation of QM, that is eventually so.

They don't, but the positions of the excited nerves determine the picture you will eventually see.